internal.h: parenthesize macro argument

* internal.h (THROW_DATA_P): parenthesize the argument which is
  casted.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58263 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

internal.h

@@ -887,7 +887,7 @@ struct vm_throw_data {
     VALUE throw_state;
 };
 
-#define THROW_DATA_P(err) RB_TYPE_P(((VALUE)err), T_IMEMO)
+#define THROW_DATA_P(err) RB_TYPE_P((VALUE)(err), T_IMEMO)
 
 /* IFUNC */